1. Field of the Invention
The present invention relates generally to a multi-hop relay broadband wireless communication system, and in particular, to an apparatus and method for transmitting control information to a Relay Station (RS) in a multi-hop relay broadband wireless communication system.
2. Description of the Related Art
In general, a mobile communication system performs communication via one direct link between a Base Station (BS) and a Mobile Station (MS) and therefore, can easily configure a wireless communication link with high reliability between the MS and the BS. However, it is difficult to provide an efficient service in radio environments where traffic distribution or telephony demand quantity is greatly varied because the flexibility of wireless network configuration is low due to a fixed position of the BS.
In order to provide a solution to this disadvantage, 4th-Generation (4G) mobile communication systems are considering the introduction of a multi-hop relay technique to forward data in a multi-hop fashion using several neighboring MSs or RSs. With the introduction of the multi-hop relay technique, the system can reconfigure a network quickly in response to the change of the neighboring environments and manage the whole wireless network more efficiently. Further, the system can provide a radio channel having a better channel state to an MS by installing an RS between a BS and the MS and configuring a multi-hop relay path via the RS according to the multi-hop relay technique. Furthermore, the system expands cell coverage by providing a high-speed data channel to an MS within a shadow area where communication with the BS is impossible, using the multi-hop relay path.
FIG. 1 shows a construction of a conventional multi-hop relay broadband wireless communication system. As shown in FIG. 1, a BS 100 connects with an MS A 110 located in a service area via a direct link. Alternatively, the BS 100 connects with an MS B 120 located outside the service area that has a poor channel state, through an RS 130 via a relay link.
That is, the BS 100 can provide a better radio channel to the MS B 120 using the RS 130 if the MS B 120 is located outside the service area that has a poor channel state or in a shadow area around a building. Accordingly, the BS 100 can provide a high-speed data channel to a cell boundary area in which a channel state is poor, using the multi-hop relay technique, and can expand cell coverage. At this time, the broadband wireless communication system relays a signal between the BS and the MS using the RS. Therefore, the broadband wireless communication system configures not only a BS and MS link but also a BS and RS link and an RS and MS link.
The conventional broadband wireless communication system using a frame of a structure of the Institute of Electrical and Electronics Engineers (IEEE) 802.16e is shown in FIG. 2.
Referring to FIG. 2, the frame includes a downlink subframe 200 and an uplink subframe 210. The downlink subframe 200 includes a preamble and a DownLink (DL) access link. The preamble is for an MS to acquire frame synchronization from a BS. The DL access link is for the BS to transmit a signal to the MS. The uplink subframe 210 includes an UpLink (UL) access link for the MS to transmit a signal to the BS. However, there is no frame interval for an RS to transmit a signal under the conventional scheme.
As described above, the frame structure of the conventional broadband wireless communication system allocates resources for the BS and MS link only. Thus, in order for the broadband wireless communication system to use a multi-hop relay technology, there is needed a frame structure that is capable of allocating resources to not only the BS and MS link but also the BS and RS link and the RS and MS link.